The invention relates to a blood collection system for collecting blood from a body part for diagnostic purposes.
For analytical diagnostic purposes, a small amount of blood is collected from a body part. This is done by using lancets, the tip of which creates a wound in a body part, preferably a finger or an earlobe. This method of collecting blood is of great importance, especially as a self-collection system for diabetic self-monitoring because it permits a greatly improved method of stabilizing the medication treatment of diabetics. This also makes it possible to prevent the serious sequelae of diabetes.
Therefore, in the state of the art there have been proposals for a plurality of instruments and lancet devices with which the puncturing procedure is performed mechanically. Normally, a spring is used to drive the puncturing movement. The depth of penetration can be defined by a stop in the housing against which the lancet or a component of the lancet drive is stopped. However, the stopping causes a considerable oscillation which prevents a uniformly clean puncture.
It has been found that with the widely used devices in which the lancet is coupled to the driving spring during the entire puncturing movement, which is made up of a forward movement phase and a retraction movement phase, post-pulse oscillation of the spring results in the tip of the lancet puncturing the body part more than once. This is undesirable, however, because it causes the patient additional pain.
This problem does not exist with more complex designs with which the driving spring is coupled to the lancet only during the forward movement phase and an additional mechanism is provided for retracting the lancet from the body part.
For example, a blood collecting device with a lancet is known from U.S. Pat. No. 6,206,901 B1; in this patent, the lancet is driven by a ram and a driving spring. The lancet here is uncoupled from the driving spring for a part of its forward movement phase. To retract the lancet, a second spring is provided near an outlet opening in the housing. This second spring is designed as a return spring and serves to retract the lancet out of the wound after the puncture step. The return spring is put under tension by the lancet only during the forward movement phase. The kinetic energy of the lancet is stored in the spring and, after reaching the maximum stress of the return spring, the kinetic energy is returned to the lancet by the spring. However, this has the disadvantage that the lancet is decelerated by the return spring. Therefore, the entrance of the lancet into the patient's skin takes place painfully and slowly.
EP 0 036 443 B1 also discloses a lancet device with which a lancet is driven by a driving spring during the forward movement phase, and the driving spring is uncoupled from the lancet during a part of the puncturing movement. To return the lancet after the puncturing operation, a second spring is provided in the area of an opening in the housing of the lancet device, moving the lancet in the reverse direction after the puncturing operation. The second spring is put under tension by the lancet only during the forward movement phase of the puncturing movement, i.e., not before the lancet strikes the second spring on the movement path in the puncturing direction. Therefore, the lancet is decelerated; its kinetic energy is converted into spring energy until the kinetic energy is completely consumed. Then, the puncturing of the lancet into the body part is again decelerated.
US 2004/0267300 A1 discloses a lancet device with which the lancet is driven by a rotating spring having a plurality of spring arms. The spring arms are put under tension. After releasing a lock, the spring arms move the lancet in the direction of an opening in the housing. After releasing the tension on the spring arms, which are designed between an outer ring and an inner ring, there is no post-pulse oscillation. To move the lancet back out of its puncture position, restoring spring arms are provided. These arms are located between the inner ring and an inside axis. The restoring spring arms are put under tension before the start of the puncturing movement. As soon as the lancet has punctured into a body part, i.e., the spring arms are completely relaxed. The restoring spring arms are also relaxed, so that the lancet is retracted out of its puncture position. Since the restoring spring arms are already prestressed, no kinetic energy of the lancet is used for applying tension to the restoring springs during the puncture movement. The puncture is thus made rapidly and with little pain. However, the mechanism of the lancet device is very complicated because an accurate cooperation of the spring arms applying tension as well as the restoring spring arms must be ensured. In addition, the rotational movement of the springs must be converted to a translational movement of the lancet.
All these known blood collecting devices have a much more complicated structure than the designs mentioned in the introduction, where the spring (usually a simple helical spring) executes a releasing movement that acts linearly in the direction of puncture and is transmitted directly to the lancet. This design principle is not only simple and therefore inexpensive, but is also space saving. It therefore allows a slender construction for the hand which facilitates handling. To implement a rapid and therefore relatively pain-free puncture of the lancet in a body part, strong driving springs are used. There is a particularly great risk that the lancet, i.e., the lancet needle might puncture the body part repeatedly due to post-pulse oscillation of the driving spring. If the driving spring is designed to be weaker, the maximum puncture depth in the skin is not ensured, in which event not enough blood is obtained.